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Astronomers on verge of finding Earth's twin
(Agencies)
Updated: 2008-06-25 15:27 The fast track To eek out even more sensitivity from current technologies, Charbonneau suggests astronomers look for worlds around small stars. He and other astronomers are in fact probing the universe for transiting planets orbiting M dwarfs, or red dwarfs, which are about 50 percent dimmer than the sun and much less massive. Red dwarfs are also considered the most common star type in the universe.
"I think the real opportunity there is to study low-mass stars, and that's because we're looking for very small planets," Charbonneau said. "The difficulty is the ratio between the planet's mass and the star's mass or the planet's size and the star's size depending on how you want to find it." The low mass and luminosity means any changes to the star due to an Earth-mass planet are much more likely to be detected. "A late M star is about 10 times smaller than the sun," said Penn State's James Kasting, who studies planetary atmospheres and the habitable zones of exoplanets. "So Earth going in front of an M star would give a 1 percent signal. That's like Jupiter going in front of the sun." Kasting added, "We could conceivably find an Earth analog planet by this method within the next five or ten years." Other teams are gearing up to look for Earth-like worlds orbiting massive stars like the sun. NASA's Kepler observatory is scheduled for launch in February 2009, after which the high-powered telescope will monitor about 100,000 stars in the Milky Way looking for periodic dimming of starlight due to a planet's transit in front of the star. The French COROT mission is already up in space working in a similar fashion. Good hunting The ultimate goal of planet-hunting projects is to find Earth twins. "We are looking for twins of the Earth, analogs that walk and talk and smell like our own Earth," Marcy said during a telephone interview. He is currently looking for super-Earths using the W.M. Keck Observatory in Hawaii. Such a twin would be rocky, with a similar chemical composition to Earth, and would orbit within the habitable zone of its star. The habitable zone defines the distance at which a planet must orbit from its star for liquid water to exist on its surface -- not too hot like Venus, not too cold like Neptune or Pluto. Astronomers have found planets orbiting pretty close to the habitable zone, but none so far within it. "I suspect there are Earth-like planets with lakes and rivers and waterfalls and deep glacial gorges and that are spectacularly beautiful," Marcy said. Life beyond Earth Finding a planet in the habitable zone is the first step toward finding alien life. "When we say it's a habitable world, all we're doing is saying it potentially could hold life," Boss said. "To go beyond that to say, 'Here's a habitable world; is it inhabited,' then you need to start studying the atmosphere of the planet." The James Webb Space Telescope (JWST), scheduled for launch in 2013, could do just that. "There might be a signal in the atmosphere that could be a smoking gun and would suggest that plate tectonics is there," said earth and planetary scientist Diana Valencia of Harvard University. Her computer models have shown that plate tectonics, the forces that move continents and lift gigantic mountain ranges, are key to life on Earth as we know it, and possibly to life on other worlds. That's because as the rocky plates that form the planet's outer shell move about, they also recycle carbon dioxide. This greenhouse gas keeps our planet's temperature balmy, but not too hot. And the telltale signal would be certain levels of carbon dioxide, suggesting that just as on Earth, this other world relies on plate tectonics to cycle carbon. But first things first. "There's no doubt that other Earths exist, simply due to the sheer vast numbers of other stars and galaxies in our universe," Marcy said. "There's a deeper question -- how common are Earth-like planets? Are Earth-like planets a dime a dozen, or are they quite rare, quirky precious planets that are one in a thousand or one in a million?"
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